Experiments will be performed on golden hamsters to identify the source(s) of peptide-immunoreactive fibers which terminate among clusters of preganglionic neurons labeled with horseradish peroxidase (HRP) transported from the intermesenteric trunk (aortic plexus). Animals will be subjected to selective chordotomies and dorsal rhizotomies to determine whether supraspinal structures and/or primary afferents contribute to these fiber systems; peptide-immunoreactive fibers will be visualized using the immunoperoxidase (PAP) method and antisera raised against leu-enkephalin, somatostatin, and substance P. The PAP technique will also be used to examine the relationships between HRP-labeled preganglionic neurons and serotonergic fibers in the lumber spinal cord. Another set of experiments will employ two retrograde tracers, HRP and 4,6-diamidino-2-phenylindole (DAPI), to determine if preganglionic neurons in the lumber cord send axon collaterals to two target ganglia within visceral regions. Pairs of visceral nerves innervating contiguous visceral structures will be isolated and the proximal cut end of each nerve will be exposed to either HRP or DAPI. The spinal cord will then be examined for preganglionic neurons containing both tracers (double-labeled cells). The results of such double tracer experiments should indicate the degree of divergence in sympathetic preganglionic outflow to the lower abdomen and pelvis.